An Internet Protocol version 6 (IPv6) over IPv4 (IPv6 over IPv4) technology is that: an IPv6 packet is encapsulated in an IPv4 packet, to implement transparent transmission of the IPv6 packet on an IPv4 network. During an initial phase of transition from an IPv4 network to an IPv6 network, IPv4 networks have been widely deployed and IPv6 networks are isolated islands dispersed around the world. It is apparently uneconomical to connect these isolated islands by using dedicated lines, and a common approach is to use a tunnel technology. The tunnel technology may be used to create tunnels on the IPv4 networks, so as to implement interconnection of the isolated IPv6 islands. This is similar to a situation in which a tunnel technology is used on an Internet Protocol (IP) network to deploy a virtual private network (VPN). An ISATAP tunnel is used in a situation in which an IPv4/IPv6 host on an IPv4 network accesses an IPv6 network, and the ISATAP tunnel may be established between the IPv4/IPv6 host and an ISATAP device. For ease of description, the IPv4/IPv6 host is uniformly referred to as an ISATAP host in the following content.
An ISATAP tunnel on a device generally serves multiple ISATAP hosts. When multiple ISATAP hosts need to order an IPv6 multicast group program on an IPv6 network, an ISATAP device needs to enable a Multicast Listener Discovery protocol (MLD) function. An ISATAP host encapsulates an MLD multicast group member join packet in an IPv4 unicast packet, and sends the IPv4 unicast packet to the ISATAP device. Because each IPv6 multicast group in MLD multicast group join information saves local link address information only of an ISATAP host that last sends an MLD multicast group member join packet, after the ISATAP device receives an IPv6 multicast data packet, the ISATAP device can only copy the IPv6 multicast data packet and encapsulate copies in IPv4 unicast packets, and the IPv4 unicast packets are forwarded to all ISATAP hosts by a device on an IPv4 network. As a result, some ISATAP hosts that do not order this IPv6 multicast group may also receive IPv6 multicast data. In addition, the IPv6 multicast data is first copied and then is encapsulated in the IPv4 unicast packets for transmission, which results in waste of bandwidth of the IPv4 network.